Nine cases of primary septic arthritis in heroin addicts are reported. Fibrous and cartilaginous joint localizations are prominent (four sternoarticular, three sacroiliac, one sacroccocygeal, and one knee). In all patients but one, conventional roentgenographic studies were negative. In six cases the causative agent was Staphylococcus aureus and in two cases, Candida albicans. In one case, it could not be determined. Our clinical observations, correlating the radioisotopic studies, suggest that in the first week of evolution the diagnostic procedure of choice is the [67Ga]citrate scintigram. Indeed, during this period the [99Tc]MDP bone scan is usually negative. The early demonstration and localization of the disease, together with the rapid bacteriologic diagnosis, allows for an early and more appropriate antibiotic treatment and better results.